What Do Genes Look Like?

1. What Do Genes Look Like? Pgs 80-87

2. Traits are determined by genes. • Genes can be passed down from generation to generation. • Genes are located on chromosomes. • Chromosomes are made of protein and DNA • DNA (Deoxyribonucleic Acid) is hereditary material that that controls all the activities of a cell, contains the information to make new cells, and provides instructions for making proteins

3. Completing the Gene Puzzle • Gene material must be able to do two things: • 1. Be able to supply instructions for cell processes or building cell structures. • 2. Be able to be copied each time a cell divides. • Scientists originally thought that protein carried this material, but then found that DNA contained this information.

4. DNA Subunits • DNA has subunits called nucleotides: • Each nucleotide is made of a sugar unit, a phosphate unit, and a base. • There are four bases: • 1. Adenine (A) • 2. Thymine (T) • 3. Guanine (G) • 4. Cytosine (C) • Each base has a different shape

5. Chargaff’s Rule • Erwin Chargaff, in the 1950’s, found that the amount of adenine in DNA always equals the amount of thymine. • Also, he found that the amount of guanine equals the amount of cytosine

6. DNA Pictures • Clues to what DNA would look like came from a chemist named Rosalind Franklin. • She used X-rays to take pictures of DNA and found that DNA is spiral shaped

7. Watson and Crick • James Watson and Francis Crick made further discoveries that the shape of DNA was actually a double helix. • A double helix looks like a twisted ladder. • The two side of the ladder are made of alternating sugar and phosphate units. • The rungs of the ladder are made of nucleotide base pairs. • Adenine always pairs with thymine. • Guanine always pairs with cytosine.

8. DNA is Copied • The base pairs are the secret to DNA’s ability to make a copy of itself. • The pairs are complimentary to each other. • A-T and C-G • The DNA will split down the middle of the base pairs and pair each side that is split to make two identical copies.

10. How does DNA have so much information? • The base pairs. • The order of the bases on a strand of DNA are like a code for instructions. • The order tells the cell what to do. • Ex. Make a copy, cellular respiration, blue eyes, etc

11. Putting it all together • Skin on your forehead • Magnified looks like different types of cells make up skin • One skin cell • Each cell contains 46 chromosomes • Each chromosome is made of DNA and protein • Each chromosome has lots of DNA in twisted strands • DNA is made of numerous loops • Each loop is made of even more coils • Each DNA molecule has two halves that are connected down the center and twisted like a spiral staircase

12. Exceptions to Mendel’s principles • As research has been done, scientists found exceptions to Mendel’s findings. • These exceptions required more research. • Some traits were not completely dominant over another • Each allele has its own degree of influence known as incomplete dominance. • Ex. The Snapdragon flower • If you cross a red flower with a white flower you get a pink flower.

14. Genes can influence other genes • A white tiger has a gene to make it white, but that gene also influences the eye color to be blue (both recessive traits)

15. Many genes influence a single trait. • Traits like skin color, eye color and hair color are the result of several genes acting together. • There may be several different shades of blue or brown eyes. • These are influenced by the different combinations of alleles acting on those traits.

16. Importance of Environment • Genes aren’t the only thing that influence your development. • Consider healthy diet and exercise. • You may have the genes to be tall and muscular, but if you don’t eat right or exercise you may not get the nutrients you need to be tall and muscular.